1. Field of the Invention
The present invention relates to an internal combustion engine.
2. Description of the Related Art
In a known internal combustion engine, the engine is provided with a fuel injection device and a purge control device(Japanese Unexamined Patent Publication (KOKAI) No. 62-20669).
Such a purge control device usually is provided with a charcoal canister having an activated carbon layer therein for adsorbing fuel vapor produced in, for example, the fuel tank, to prevent fuel vapor from being discharged into the outside air. When a purging operation is to be carried out, fuel vapor adsorbed by the charcoal canister is desorbed and fed into the combustion chamber of the engine. If the purging operation is carried out while the engine is idling, the idling speed of the engine may be increased above an acceptable limit. However, if the purging operation is stopped in order to maintain the idling speed of the engine within the acceptable range, the charcoal canister of the purge control device may become saturated with fuel vapor. This then results in the discharge of fuel vapor into the atmosphere.
In an another known internal combustion engine, when the engine is operating under a light load, an air-fuel mixture is formed in a restricted region in the combustion chamber. The remainder of the combustion chamber is filled with air, and the air-fuel mixture is ignited by the spark plug. Conversely, when the engine is operating under a middle load or under a high load, the entire interior of the combustion chamber is filled with an air-fuel mixture(Japanese Unexamined Patent Publication (KOKAI) No. 4-194354). Such an engine is also provided with the above-mentioned purge control device.
In such an engine, if the purging operation is carried out while the engine is idling, fuel vapor spreads into the air in the combustion chamber and a large portion of the fuel vapor may be discharged into the exhaust passage of the engine without being burned in the combustion chamber. If the purging operation is stopped while the engine is idling in order to prevent fuel vapor from being discharged into the exhaust manifold air without being burned in the combustion chamber, the charcoal canister of the purge control device may become saturated with fuel vapor. Thus the adsorbing capacity of the charcoal canister is reduced and fuel vapor may be discharged into the outside air without being adsorbed by the charcoal canister.